This invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to processes for the preparation of toner compositions. In one embodiment, there are provided in accordance with the present invention in situ processes for the preparation of toner compositions with average volume particle sizes equal to, or less than about 12 microns in embodiments, and excellent narrow geometric size distribution (GSD) characteristics, such as in the range of from about 1.2 to about 1.4 in embodiments without resorting to classification. In embodiments, the process of the present invention comprises microdroplet swelling and wherein, for example, a second monomer is added to a microdroplet containing a monomer or monomers, pigment and optionally a charge controlling agent prior to polymerization thereof. In embodiments thereof, the processes of the present invention comprise dispersing an organic phase comprised of a monomer or plurality of monomers, pigment, and optionally a charge controlling agent in an aqueous medium containing a surfactant, such as hydroxyethyl cellulose, and thereby generating organic microdroplets of average volume particle sizes of about 5 microns to about 15 microns and GSDs of from about 1.4 to about 1.7; thereafter adding a second monomer which is preferably a gas at ambient temperature, such as butadiene, and whereby the said second monomer swells or is absorbed by the microdroplets such that a narrowing of geometric size distribution results such as from about 1.2 to about 1.4; followed by polymerization of the monomers by heat and separating the toner by washing and drying. With the process of this invention, encapsulated toners comprised of a core resin, colorant, optionally a charge control agent and a shell thereover comprised of a polyurea, a polyester, a cellulose coating and the like can be prepared with high yields, such as from about 90 percent to about 100 percent, and wherein average volume particle sizes of less than about 10 microns and excellent narrow geometric size distribution (GSD) characteristics, such as from about 1.2 to about 1.4 are obtained without classification. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic imaging and printing processes, including color processes.
In reprographic technologies, such as xerographic and ionographic devices, toners with small average volume diameter particle sizes of from about 5 microns to about 20 microns are utilized. Moreover, in some xerographic machines, such as the high volume Xerox Corporation 5090 printers, high resolution characteristics and low image noise can be attained utilizing small sized toners with average volume particle of less than 11 microns and preferably less than about 7 microns and with a narrow geometric size distribution of less than about 1.4 and preferably less than about 1.3. The volume average particle size is the 50 percent value of the volume distribution curve, and the geometric size distribution is reported as the square root of the 84 percent volume particle size divided by the 15 percent volume particle size. Generally, it is observed that toners with broad GSDs, such as from about 1.5 to about 1.7 or more, can result in reduced image quality such as low resolution and high image noises, whereas toners with narrow GSDs, such as less than 1.4 and preferably less than 1.3, can result in superior copy quality with high resolution and low undesirable image noises, that is for example minimal or no background deposits, excellent line resolution with minimal or no image deterioration, or background deposits.
Numerous processes are known for the preparation of toners, such as for example conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with an average volume particle diameter of from about 7 microns to about 20 microns and with a broad geometric size distribution of from about 1.4 to about 1.7. In such processes, it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.4 are attained. However, in the aforementioned conventional process, low toner yields after classifications may be obtained. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. Additionally, during the preparation of smaller sized toners with particle sizes of from about 7 microns to about 11 microns, lower toner yields are obtained after classification, such as from about 50 percent to about 70 percent. With the processes of the present invention in embodiments, small average particle sizes of from about 3 microns to about 9, and preferably 7 microns with excellent GSDs of from about 1.2 to about 1.4 are attained without resorting to classification processes, and wherein high toner yields are attained such as from about 90 percent to about 98 percent. Additionally, other processes such as suspension polymerization, or semisuspension and the like, are known, wherein the toners are obtained by dispersion of an organic mixture in an aqueous surfactant solution and thereafter polymerized by heating to yield encapsulated toners of average particle diameter of from between about 5 to about 20 microns and a geometric size distribution of from about 1.33 to about 1.7 after classification. With the processes of the present invention, in embodiments a second monomer, which is preferably a gas at ambient temperature such as butadiene, is added to a microdroplet suspension prior to polymerization. It is believed that during this process step the smaller microdroplet particles absorb the second monomer at a faster rate than the larger particles present due to the greater surface area of the smaller particles, hence resulting in a narrowing of geometric size distribution such as from about 1.2 to about 1.4. Processes are also known wherein particles are prepared by solvent dispersion processes providing monodispersed GSDs such as from about 1.01 to 1.13. However, such processes are limited to selected monomers, employ undesirable organic solvents and are difficult to pigment or dye.
More specifically, the processes of the present invention involves (i) mixing a core resin forming monomer(s) such styrene and n-butyl acrylate, a colorant such as HELIOGEN BLUE.TM., a free radical initiator such as VAZO 67.TM., and optionally a charge control agent such as chromium salicylate; (ii) dispersing this mixture using a high shearing device such as a Brinkmann 45G probe operating at from about 8,000 to about 10,000 rpm for a duration of from about 30 to about 120 seconds, in a vessel containing an aqueous solution of a surfactant such as TYLOSE.RTM. and optionally an ionic surfactant such as sodium dodecylsulfate and generating a microdroplet suspension of an average volume particle size of from about 3 to about 15 microns with GSD's of about 1.4 to about 1.7; (iii) adding a second monomer such as butadiene such that the said second monomer swells or is absorbed by the smaller microdroplet particle at a faster rate than the larger microdroplet particles resulting in the narrowing of geometric size distribution to less than 1.4 and preferably less than about 1.3; (iv) heating the mixture to effect free radical core polymer formation at from about 60.degree. C. to about 120.degree. C. for a duration of from about 360 minutes to about 720 minutes; and (v) washing the toner product by centrifugation from about 4 to about 6 times, and drying using preferably a fluidized bed, operated at from about 30.degree. C. to about 60.degree. C. for a duration of from about 240 minutes to about 480 minutes. Additives to improve flow characteristics may be optionally added to the toner such as AEROSIL.RTM. or silicas and the like in an amount of from about 0.1 to about 10 percent by weight of the toner.
Encapsulated toners and processes thereof are known; for example, there are disclosed in both U.S. Pat. Nos. 4,338,390 and 4,298,672, the disclosures of which are totally incorporated herein by reference, positively charged toner compositions with resin particles and pigment particles, and as charge enhancing additives alkyl pyridinium compounds. Moreover, toner compositions with negative charge enhancing additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. Additionally, other documents disclosing toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014 4,394,430, and 4,560,635 which illustrates a toner with a distearyl dimethyl ammonium methyl sulfate charge additive. These toners may be prepared, for example, by the usual known jetting, micronization, and classification processes. Toners obtained with these processes generally possess a toner volume average diameter of from between about 10 to about 20 microns and the GSDs of these toners are usually from about 1.3 to about 1.45 after classification and are believed to be obtained in yields of from about 70 percent to about 85 percent by weight. The toners obtained with the processes of the present invention in embodiments are prepared by monomer swelling processes, and alleviate the need for classification and results in average particles sizes of about 3 to about 15 microns with GSDs of about 1.2 to about 1.4 with high toner yields of, for example, 90 percent to about 99.5 percent by weight.
Moreover, encapsulated toner compositions and process are also known, as illustrated for example in U.S. Pat. No. 4,954,412, the disclosure of which is totally incorporated herein by reference, and which illustrates a suspension process for an encapsulated toner comprised of core resin, a pigment and a shell comprised of a polyester, see Example 1, column 16 line 11, and similarly Examples 2 through Example 10, wherein the GSD is reported to be from about 1.31 to about 1.62. Similarly, U.S. Pat. No. 4,937,167 discloses a suspension process for an encapsulated toner comprised of a core material comprising a resin, colorant and a shell comprising a polyurea, see Examples 1 through Examples 9, wherein the GSD is reported to be from about 1.4 to about 1.62. Additionally, U.S. Pat. No. 5,223,370, the disclosure of which is totally incorporated herein by reference, discloses an in situ suspension process for a toner comprised of a core comprised of a resin, pigment and optionally charge control agent and coated thereover with a cellulosic material, and wherein the GSDs are reported to be from about 1.32 to about 1.45. The process for the encapsulated toners of the present invention differs from these processes in that, for example, during the suspension process, a second monomer is swelled into the microdroplet prior to polymerization, thus effecting a narrowing of the GSD, which can be caused by the larger surface area of the smaller particles, hence a growth in particle sizes of the smaller particles and narrowing of GSD of from about 1.2 to about 1.4 and preferably less than 1.3. Similarly, U.S. Pat. Nos. 4,789,617; 4,601,968; 4,592,990; 4,904,562; 4,465,756; 4,468,446; 4,533,616; 4,565,763 and 4,592,990 also disclose suspension processes for the preparation of encapsulated toners with GSDs usually above 1.35 to about 1.6. Other prior art encapsulated toners include pressure fixable encapsulated toners and processes, reference U.S. Pat. Nos. 4,803,142; 4,656,111; 4,517,273; 4,543,312; 4,609,607; 4,784,930; 4,307,169; 4,617,249 and 4,702,989.
There is a need for black or colored toners wherein small particle sizes of less than or equal to 10 microns in volume diameter and narrow geometric size distribution of less than 1.4 and preferably less than 1.3 are obtained. Furthermore, there is a need for colored toner processes wherein the toner synthetic yields are high, such as from about 90 percent to about 100 percent, without resorting to classification procedures. In addition, there is a need for black and colored toners that are nonblocking, enable excellent image resolution, are nonsmearing, and of excellent triboelectric charging characteristics.